Hithertofore, thermosetting molding resins, principally diallyl phthalate resins (DA), alkyd resins and phenolic resins, have been employed in the electrical/electronics industry where a high level of arc resistance, tracking resistance together with excellent mechanical, chemical and thermal properties are necessary. However, thermosetting molding resins are more difficult to process than thermoplastic resins, since they usually require higher molding temperatures or longer cycle times, or both. Furthermore, articles molded from thermosetting molding resins cannot be recycled and remolded. For these reasons, it is desirable to supplant the earlier-developed thermosetting materials in electrical/electronics applications with thermoplastic molding compositions. Until the present invention, there are no known thermoplastic molding compositions which retain sufficiently high levels of arc resistance and tracking resistance to replace the thermosetting molding resins in the area of electrical switches, such as circuit breakers, wherein a very high level of arc resistance and tracking resistance is needed.
Thermoplastic polyesters, such as polybutylene terephthalate, are known to provide excellent molding compositions. Such compositions can be molded at low to moderate temperatures and rapid cycle times, to give molded articles having superior chemical resistance, thermal stability and product appearance, together with good mechanical strength, stiffness, low friction and wear properties and good resistance to fracture.
Numerous patents including British Pat. No. 1,060,401, published Mar. 1, 1967 and assigned to Kurashiki Rayon; Belgian Patent No. 747,243, issued Sept. 14, 1970 to Celanese Corporation; and U.S. Pat. No. 3,953,394, issued Apr. 27, 1976 to Fox and assigned to General Electric Company disclosed blends of polybutylene terephthalate and polyethylene terephthalate. Such blends can also include known reinforcing agents and flame retardants.
It is further known that the mechanical strength and processibility of polyester resins and resin blends can be improved by the incorporation of fiber glass and talc. The use of these additives for this purpose is disclosed, for example, in U.S. Pat. No. 3,931,094, issued Jan. 6, 1976 to Segal et al and assigned to Allied Chemical Corp.; U.S. Pat. No. 4,113,692, issued Sept. 12, 1978 to Wambach and assigned to General Electric Co.; U.S. Pat. No. 4,212,791, issued July 15, 1980 to Avery et al and assigned to Rohm and Haas; U.S. Pat. No. 4,257,937, issued Mar. 24, 1981 to Cohen and U.S. Pat. No. 4,267,286, issued May 12, 1981 to Campbell and both assigned to General Electric Co.; U.S. Pat. No. 4,271,063, issued June 2, 1981 to Borman et al and U.S. Pat. No. 4,271,064, issued June 2, 1981 to Dieck and both assigned to General Electric Co.; U.S. Pat. No. 4,277,391, issued July 7, 1981 to Charles and assigned to GAF Corp.; U.S. Pat. No. 4,280,005, issued July 21, 1981 to Fox and assigned to General Electric Co.; and U.S. Pat. No. 4,284,550, issued Aug. 18, 1981 to Mizuno et al and assigned to Dainippon Ink and Chemicals Inc.
Flame retardant polyester resin compositions are disclosed in, among others, U.S. Pat. Nos. 3,931,094; 4,113,692; 4,212,791; 4,257,937; 4,267,286; 4,271,063; 4,271,064; and 4,284,550 mentioned above. The use of decabromobiphenylether as one component of an effective flame retardant additive package for polyester molding resins is specifically disclosed in U.S. Pat. Nos. 3,971,752, issued July 27, 1976 to Aoyama and assigned to Toray Ind., Inc.; 4,280,005, mentioned above; and in Defensive Publication T918001. The use of polytetrafluoroethylene as a drip suppressant is disclosed in U.S. Pat. No. 3,671,487, issued June 20, 1972 to Abolins and assigned to General Electric Co.
U.S. Pat. No. 3,624,024 issued Nov. 30, 1971 to Caldwell and assigned to Eastman Kodak Co. discloses that incorporating talc into flame retardant polybutylene terephthalate compositions containing a brominated additive can increase the heat distortion temperature of articles molded therefrom.
Polyester resin molding compositions with improved arc resistance are described, for example, in U.S. Pat. No. 4,052,356, issued Oct. 4, 1977 to Breitenfellner et al and assigned to Ciba Geigy A.G. This patent discloses reinforced polybutylene terephthalate compositions containing kaolin from which molded articles having an arc resistance of 80-125 sec. and a tracking resistance of 250-275 volts can be obtained. U.S. Pat. No. 4,035,333, issued July 12, 1977 to Kamada et al and assigned to Mitsubishi Rayon Co. Ltd., discloses that polybutylene terephthalate molding compositions containing sodium antimonate or a sodium antimonateantimony trioxide mixture together with talc provide molded articles having improved arc resistance. Japanese Published Patent Application No. 52-58752/1977 discloses flame resistant polyester molding compositions containing mineral fillers and fiber glass to provide a resin with an improved arc resistance.
It has been found that flame retardant polybutylene terephthalate resin compositions filled with approximately 30 to 60 percent by weight of fiber glass and talc will provide articles molded therefrom with an arc resistance of at least 150 sec. and a tracking resistance of at least 400 volts. However, it was also found that the high level of arc resistance obtained initially decays over time to a level where the usefulness of the resin would be impaired.
There is, thus, a need for an improved flame resistant thermoplastic polyester resin composition with a sustained high level of arc resistance and tracking resistance, either of which will not substantially decay over time.
It is, therefore, an object of the invention to provide an economical thermoplastic resin material which retains a high level of arc and tracking resistance for use in the electrical and electronics industry as parts for electrical switches, such as circuit breakers and the like.
It is another object of the invention that the thermoplastic resin molding material possesses superior mechanical strength, stiffness and good resistance to fracture.
It is a further object of the invention that the thermoplastic resin molding mateial possesses superior chemical resistance, thermal stability and product appearance.
It is also an object of the invention to provide a thermoplastic resin molding material which is processible at low to moderate temperatures with rapid cycle times.
It is a further object of the invention to provide a thermoplastic resin material which will be flame resistant especially under use conditions when subjected to high voltage or high current.
It is also an object of the invention that the thermoplastic resin material will be highly resistant to the passage of electricity on its surface when a high voltage of electricity is applied to conductors imbedded in the resin material, i.e., the resin has a high level of arc resistance, at least 150 sec. and a high level of tracking resistance, at least 400 volts.